Lanza’s brother, Ryan, 24, who was earlier named in error as the killer, was being questioned by police last night.

And there were reports that a body, understood to be the brothers’ father, had been found at an address in nearby New Jersey.

State police spokesman Lieutenant Paul Vance said 18 children had been pronounced dead at the scene and two died in hospital.

There were six adult victims at the school, along with the gunman. The shots were all fired in two rooms in one area of the school.

Vance, who would not officially confirm Lanza’s identity, added there was also a secondary crime scene in Newtown, where the body of an adult had been found.

The massacre unfolded early in the school day in the normally peaceful community 60 miles north-east of New York City.

Jessica Hill/AP

A woman waits for news oafter the shooting

Police said Lanza entered the school wearing dark clothing, a mask and a bullet-proof vest, and was carrying four guns.

It is understood two other guns, believed to be registered to Lanza, were found in a car nearby.

Police were called to the school at 9.41am after reports of shots in one of the kindergarten classrooms.

Witnesses said that Lanza fired more than 100 shots at the terrified pupils and staff.

As police searched the school, guns drawn, other officers ushered terrified youngsters, many in tears, to safety away from the building.

Photos from the scene showed pupils being escorted through a car park in a line, hands on each other’s shoulders.

A police officer leads children from the Sandy Hook Elementary School

One nine-year-old child told the local newspaper: “We were told to hold each other’s hands and to close our eyes. We opened our eyes when we were outside.”

One child was seen being carried from the school by a police officer, apparently seriously wounded.

Three people were taken to a nearby hospital but there were no details of their ages or injuries last night.

It was unclear whether they included the two children who died in hospital.

At the height of the alert, hundreds of officers and police dogs had the area surrounded as they worked to secure the scene.

The children were taken to a nearby fire station, where they were reunited with their parents.

The school principal, 47-year-old Dawn Hochsprung, and a school psychologist were reported to be among the dead.

Distressed parents who arrived to pick up their children spoke of their harrowing accounts of the carnage.

A young boy is comforted outside Sandy Hook Elementary School after the shooting

Brenda Lebinski, the mum of an eight-year-old girl at the school, said that her daughter is safe thanks to one teacher’s decision to move her charges into a walk-in cupboard to escape the gunman.

Mrs Lebinski said she had spoken to her daughter’s teacher, who was in the school at the time of the shooting, and that she said a masked gunman had been involved

“My daughter’s teacher is my hero,” Lebinski said.

“She locked all the kids in a closet and that saved their lives. Everyone was in hysterics – parents, students.

“There were kids coming out of the school bloodied. I don’t know if they were shot, but they were bloodied.”

Stephen Delgiadice said his eight-year-old daughter heard two big bangs and teachers told her to get in a corner.

“It’s alarming, especially in Newtown, Connecticut, which we always thought was the safest place in America,” he said.

Mergim Bajraliu, 17, who lives near the school, heard the gunshots echo from his home and raced to check on his nine-year-old sister, who was at the school.

He said his sister, who was fine, told him she had heard a scream come over the intercom at one point.

Teachers were shaking and crying as they came out of the building.

“Everyone was just traumatised,” he said.

Parent Robert Licata said his six-year-old son was in class when the gunman burst in and shot the teacher.

“That’s when my son grabbed a bunch of his friends and ran out the door,” he said. “He was very brave. He waited for his friends.”

Another mother told reporters that her child said there were bullets whizzing by him in the hallway and that a teacher pulled him into a classroom.

Terrified parents rushed to the school, desperately trying to reach their children as hundreds of officers swarmed over the premises.

Relatives react outside Sandy Hook Elementary School following a shooting in Newtown

For some, there was no happy reunion. The parents of the victims gathered , inconsolable at their loss, in the fire station close to the school during the afternoon.

Connecticut governor Dan Molloy met them there to pass on his sympathies and offer help.

Newtown is a small and affluent community in one of the richest states in the US.

Locals describe it as a “quaint New England town” which does not have the gun culture common in some parts of the US.

Mark Hertz, a reporter for a local radio station, said there was a particular sense of shock as people are not used to such tragedies.

He added: “This school is incredibly highly rated. People come to these communities for safety and a sense of quiet. It’s a feeling of invasion into the feeling of safety they have there.”

The murderous rampage will ignite a new debate on American gun control.

Assault rifles were banned in 1994. But the law was repealed in 2004.

Earlier this year, Obama called for restrictions to keep mentally unbalanced people from buying weapons, saying such a step was common sense.

In 1990, polls showed that a substantial majority of Americans, nearly 80 per cent, supported stricter limits on guns.

But gun rights groups are a powerful lobby in the US, where easy access to guns is a way of life in many of the more conservative and rural areas.

The right to bear arms is guaranteed by the US constitution, alongside such basic rights as free speech and freedom of religion.

But in a speech, Obama said: “I believe a lot of gun owners would agree that an AK-47 belongs in the hands of soldiers, not in the hands of criminals – that they belong on the battlefield of war, not on the streets of our cities.”